Before the frame timbers can be assembled into window or door frames, they must be machined accurately to length and their ends also provided with tongues and grooves or so-called mini-joint. Woodworking machines of the kind initially referred to serve mainly for end machining of frame timbers, in which the adjoining frame timbers include an angle other than 90.degree., as is the case with slanted windows or arch windows assembled from segments. The particular difficulty in end machining frame timbers for slanted windows and segmented arches consists in that the frame timber in question shall actually have the desired length after machining the two ends. In woodworking machines it is customary to get the desired length by adjusting a length stop with the aid of a millimeter scale. These simple length stops do not work however when the work table is pivoted about an axis removed from the saw plane, since the end of the timber to be machined is removed to a greater or lesser extent from the saw plane on pivoting the work table. For this reason the pivot axis is arranged at the line of intersection of the saw plane and the vertical plane running through the vertical fence surface in the woodworking machine of the kind initially refereed to (DE 2 161 385 A1).
In one such known woodworking machine (DE 2 161 385 A1) the saw unit and the moulding unit are arranged stationary on the machine frame. There is provided a work table movable relative to the machine frame. The graduated fence is supported and pivotally mounted on this work table. To this end two curved guide rails are connected fast to the work table, each having a curved guide slot. The graduated fence has two tongues, in each of which is arranged a bolt with a wing nut. Each of these two bolts engages in one of the two guide slots. By means of the bolts and the wing nuts the graduated fence can be fixed in the currently set angular position relative to the guide rails and hence relative to the work table. In order that the bolts can be moved in the curved guide slots after the wing nuts have been released, a certain amount of play is necessary. However, even the slightest amount of play affects the accuracy since the pivot axis of the graduated fence determined by the curved guide slots can be displaced simply as a result of this play. The length set by the length stop and also the set angle are then no longer correct. This has the result that both the mitre angle and the length are no longer correct in the frame timber as finally machined. On assembling a plurality of frame timbers into a circular arch the errors accumulate. Furthermore, in the known woodworking machine the graduated fence is formed as a U-shaped fence bar in which the two U-arms are disposed horizontally and the U-web forms the vertical fence surface. The two U-arms serve alternately to support the frame timber, which is pressed down by two clamping cylinders each arranged on the opposite U-arms. Since the two U-arms approach the saw plane from their datum position extending perpendicular to the saw plane and would thus get into the working region of the saw and also the moulding unit, the U-arms must have a larger spacing from the saw plane. This again has the disadvantage that the frame timber is insufficiently supported at the end to be machined. Moreover the known woodworking machine requires a relatively large amount of space for its installation, since there does not only have to be enough space for the movement of the work table but also for the frame timber usually projecting a great length off the work table, whereby this space requirement is increased so that the frame timber can be arranged in various angular positions relative to the saw plane. Moreover there is an increased risk of accident from the frame timber projecting far beyond the work table and which is moved together with the work table during the end machining, if the whole possible working space is not fenced off.
In a similarly formed known woodworking machine (DE 3 717 731 A1) a roller carriage, which carries the actual work table, is movable relative to the machine frame. The work table has a graduated fence for the frame timber fixedly connected thereto. The pivot axis of the work table should lie in the plane in which the side surface of the circular saw blade facing the frame timber moves. Since the pivot axis would thus be located in the working range of the circular saw, the facing surfaces of the work table and the roller carriage are provided with interengaging parts of an arcuately formed curved guide. The guide has a radius which corresponds to the distance of the guide from the pivot axis. This kind of pivotal mounting of the work table is however relatively expensive to make, since both the work table and the roller carriage have to be provided with interengaging arcuately formed guides, which have to be machined very accurately; moreover cylindrical rollers have to be provided between the guides in order to reduce the friction. Also this known woodworking machine needs a relatively large space for its installation, like the initially described woodworking machine. Since the work table always approaches the saw plane with its sides on pivoting out of its datum position extending perpendicular to the saw plane and would thus get into the working region of the circular saw, the work table must have a larger spacing from the saw plane. This has the disadvantage that the frame timber is inadequately supported at the end to be machined or short frame timbers can even not be machined.
In another known woodworking machine for end machining frame timbers (DE 8 907 800 U1) a graduated fence is mounted on a work table pivotal about a vertical pivot axis. The pivot axis of the graduated fence is here given a greater spacing from the saw plane. A length stop is slidable and adapted to be fixed in position on the graduated fence. There are three different electrical transducers, of which one determines the angle of rotation of the pivot axis, a second the distance of the stop from the pivot axis and a third the distance between a predetermined datum point on the work table and the tool. The measuring signals of these three transducers are fed to an evaluating and processing unit, in which calibration signals are so processed together with the measured signals that the adjustment of the machine to the workpiece to be machined is effected manually in accordance with the display of a display terminal or automatically through positioning units controlled by the evaluating and processing unit. This woodworking machine is relatively complex in its construction on account of the required computer. Still more complex is the construction when the machine is to be adjusted fully automatically by the computer through positioning units. With manual adjustment the operation is troublesome since the desired length measurement must firstly be keyed in. Only then can the position to be set for the length stop be read off the display of the computer and the length stop be adjusted.
The invention is based on the problem of providing a woodworking machine for end machining frame timbers, especially for window and door frames, of the kind initially referred to, which is of simple construction and simple to operate, facilitates precise machining to measure of the frame timbers and also ensures good support for the frame timber in the vicinity of the end to be machined.
This is achieved according to the invention in that a pivotal bearing containing the vertical pivot axis is arranged above the working region of the circular saw blade and the cutters on a support frame connected to the work table or the machine frame, in that a vertical frame with a cantilevered arm is provided on the graduated fence, the free end of which arm is connected to the pivot axis, and in that the longitudinal side of the table facing the saw plane and extending parallel thereto extends closely up to the saw plane.
Through the arrangement of the pivot bearing above the working region of the circular saw blade and of the cutters and the connection of the graduated fence through a vertical frame with cantilevered arm, the woodworking machine is relatively simple in construction and also facilitate precise machining to measure. The pivot axis of the graduated fence lies precisely at a side surface of the frame timber to be machined at the tip of the mitre to be machined and is also fixed exactly in its position. For this reason the zero point of the millimeter scale, with reference to which the length stop provided on the graduated fence is adjusted, always lies in the extension of the pivot axis and the current millimeter setting of the length stop corresponds to the desired length of the frame timber. The finished machined frame timber then has the length set on the millimeter scale independent of the angular setting of the graduated fence. The operation of the new woodworking machine is thus very simple. Since the graduated fence is pivoted relative to the work table, the longitudinal table side facing the circular saw blade can extend close up to the saw plane. Through this good support of the frame timber up to the immediate vicinity of the end to be machined is ensured in any angular setting of the graduated fence. Very short frame timbers can thus be machined at the ends with the woodworking machine.
An especially advantageous form of the woodworking machine according to the invention consists in that there is provided near the longitudinal table side facing the saw plane above the support surface of the work table a clamp beam for the frame timber, extending parallel to the longitudinal table side and adapted to be raised and lowered. With this clamp beam it is in fact possible to clamp any frame timber to be machined in the immediate vicinity of the end to be machined, independent of the angular setting of the fence bar, without any kind of adjustments having to be made to the clamping device.